1. Technical Field
The present invention relates to an optical module for an atomic oscillator and an atomic oscillator.
2. Related Art
In recent years, an atomic oscillator using coherent population trapping (CPT) as a quantum interference effect has been proposed, and downsizing of the device and reduction in power consumption have been expected. An atomic oscillator using CPT is an oscillator using a phenomenon (an electromagnetically induced transparency (EIT) phenomenon) that exists if an alkali metal atom is irradiated with two resonance lights with respective wavelengths (frequencies) that are different from each other simultaneously. As a result, absorption of the two resonance lights stops. For example, in JP-A-2009-89116, there is described an atomic oscillator as an atomic oscillator using CPT, which is configured to include an optical module having a light source for emitting coherent light, a gas cell for encapsulating alkali metal atoms, and a light receiving element for detecting the intensity of the light transmitted through the gas cell.
In the atomic oscillator using CPT, a semiconductor laser is used, for example, as the light source. In the atomic oscillator using the semiconductor laser as the light source, the drive current of the semiconductor laser is modulated to thereby cause a sideband wave in the light emitted from the semiconductor laser, and thus the EIT phenomenon is developed.
However, the light emitted from the semiconductor laser (the drive current of which is modulated) includes not only the sideband wave but also a fundamental wave (a carrier wave) having a center wavelength making no contribution to the EIT phenomenon. If the alkali metal atoms are irradiated with the fundamental wave, there is a case in which the wavelength (the frequency) of the light absorbed by the alkali metal atoms varies (the AC Stark effect) to thereby degrade the stability of the frequency of the atomic oscillator.